Extrusion apparatus and method for orienting plastic material by using an extrusion apparatus

ABSTRACT

An extrusion apparatus including at least one conical stator, and at least one conical rotor. The rotor is adapted for defibering or orienting a plastic material. The apparatus has an opening for receiving an elongate product or mandrel. The product or mandrel may be disposed in the apparatus such that, with the product or mandrel received in the opening, an extrusion conduit is defined in the opening between the product or mandrel and the rotor and stator. The rotor and stator are disposed with respect to one another to form a supply opening wherein the plastic material flows between the stator and rotor and is pressed into the extrusion conduit. A method for extrusion is also described involving the apparatus;

FIELD OF INVENTION

The invention relates to an extrusion apparatus for preparing acylindrical plastic product or for coating the product at least with onelayer of plastic, the extrusion apparatus comprising at least oneconical stator, at least one conical rotor, and at least one conicalsupply opening between them for pressing the plastic material to beextruded into an extrusion conduit. The invention also relates to amethod for defibering and/or orienting a plastic material during themanufacture or coating of a cylindrical plastic product with theaforementioned extrusion apparatus. The cylindrical plastic product maybe for example a plastic pipe, a plastic film or some other similarproduct.

BACKGROUND OF INVENTION

Previously when pipes were coated, an outer pipe was first formed on topof the pipe to be coated. In such a case, it was not possible to providethe outer pipe with the desired orientation, for example. Further, whena long screw is used in the present manner, the pipe to be coated warmsup.

Norwegian Published Specification 159,841 discloses a crosshead toolprovided with a rotating mandrel in connection with the extruder. Withthis arrangement, it is possible to form, but not maintain, the desiredorientation during the coating of a cable, even though the coating layercan be pressed at least in principle against the cable with pressure, sothat the adhesion of the coating to the surface to be coated can beimproved.

The purpose of the present invention is to avoid prior art problems andto produce an extrusion apparatus that provides the product with theprimarily desired permanent orientation.

SUMMARY OF INVENTION

This aim is achieved with an apparatus according to the invention, whichis mainly characterized in that at the end of the rotor there are meansfor defibering and/or orienting the plastic material.

The aforementioned means most preferably comprise a substantiallycylindrical extension that extends to the extrusion conduit at the endof the rotor.

These means may also comprise openings extending through the rotorand/or its extension.

There may be an annular flange at the end of the rotor or its extension,the flange preferably comprising bores extending through it.

The method according to the invention is in turn characterized mainly inthat the rotor or rotors are rotated so rapidly that the helicalorientation has almost the same direction as the circumference, and thatthe cylindrical plastic product exiting the extrusion apparatus is drawnwith a drawing device in such a way that the orientation of the plasticmolecules in the circumferential direction is reduced, so that theorientation angle of the finished product is smaller, preferably about50 to 60° .

With the rotor formed in the manner according to the invention, theplastic material to be extruded can be provided with helical orientationthat can be made permanent by cooling the pipe or the piece to be coatedin a suitable manner and possibly by also cooling the extrusionapparatus from the outside. The helical orientation is mainly producedby the motion of the rotating rotor and the helicity can be maintainedby means of the cylindrical extension. The orientation is improved bythe possible interior cooling of the material to be extruded.

An essential feature of the present invention is that the extrusionproduct can be cooled into the product form at the same time as it iscrystallized, i.e. the apparatus discharges a finished product thatthereafter does not necessarily have to be subjected to any operationsfor increasing its strength. However, the radial orientation ispreferably improved by treatment with a mandrel, and the axialorientation is adjusted with a drawing device to the desired level,which is preferably about 50% lower than in the radial direction.

An advantage of the invention is that, when several relatively thinlayers are prepared, they can be cooled and the orientation can thus befrozen. This is both very expensive and difficult with the conventionalextrusion techniques. In the arrangement according to the invention, itis possible for example to prepare two thin layers and to perform theintercooling with one machine and to manufacture more layers withanother machine. Due to the compact structure of the machine, the savingin space and money is significant.

For the purpose of supplying preferably several thin layers of plastic,the extrusion apparatus comprises at least two rotors provided with forexample cylindrical extensions and stators surrounding the rotors, thedirections of rotation of successive rotors being mutually opposite. Insuch a case, it may also be preferable that between the rotors there areintercooling apparatuses for ensuring that the orientation of the thinlayers is frozen.

Especially when plastic material is being spun, crystallized orcross-linked, it is advantageous that the cylindrical extension of atleast one rotor enlarges substantially conically in the direction offlow of the plastic material, and that there are means for conductingthe plastic material that flows in the supply opening at the back of therotor to the outer surface of the extension and thus to be mixed withthe plastic material flowing in the supply opening at the front of therotor, and that there are means for conducting the plastic material onthe outer surface of the extension further through the extension andinto its interior.

If the extrusion apparatus is intended for coating an existent product,for example a cable, the inlet end of the extrusion conduit preferablycomprises a cooling device for the initial cooling of the productconducted into the conduit.

On the other hand, if the extrusion apparatus is intended for theproduction of a plastic pipe, the extrusion conduit is provided with acooling mandrel.

In a preferred embodiment of the method according to the invention, acylindrical preform that exits the extrusion apparatus is drawn with adrawing device over a tempered mandrel following the extrusion apparatusin such a way that the stretching of the plastic molecules in thecircumferential direction increases further, but due to the simultaneousaxial stretching, the orientation angle has a value that is below theoriginal, preferably the aforementioned 50 to 60° .

The plastic material fibers can be spun and crystallized on a productmoving through a cold mandrel or extrusion apparatus.

The mixture of cross-linked and non-cross-linked plastic material can beheated to the cross-linking temperature by means of a hot mandrel.

It is also possible to start the method at a higher temperature and toform a product with a standard diameter that is drawn to the otherdevices, such as a cooling basin, in the production line, whereafter themanufacturing temperature of the product is lowered near the orientationtemperature, so that the orientation can be made permanent.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in greater detail withreference to the accompanying drawings, in which

FIG. 1 shows an extrusion apparatus provided with two rotors,

FIG. 2 shows the starting of a process in connection with an extrusionapparatus according to the invention,

FIG. 3 shows an extrusion apparatus provided with one rotor,

FIGS. 4 to 6 show embodiments of the rotor extension and itssurroundings,

FIGS. 7 and 8 show additional applications of an extrusion apparatusaccording to the invention, and

FIGS. 9 to 13 show alternative embodiments of the rotor.

DETAILED DESCRIPTION

FIG. 1 shows an extrusion apparatus according to the invention forpreparing a plastic pipe comprising several thin plastic layers or forcoating a product, such as a cable or a tube, with several thin plasticlayers. This extrusion apparatus comprises two conical rotors 1 and 2,stators 3, 4 and 5 that separate the rotors from each other and surroundthem, and supply openings 6, 7, 8 and 9 between the rotors and thestators for pressing the plastic material M to be extruded into anextrusion conduit 10. The extrusion conduit 10 is formed in this case ofan annular space situated between an opening extending through theextrusion apparatus and a cooling mandrel 11 pushed through the opening.The cooling mandrel 11 can be used at least in a case where a newmultilayer pipe is being formed on it.

The rotors 1 and 2 are arranged to rotate in opposite directions, andeach rotor comprises a cylindrical extension 12, 13 extending to theextrusion conduit 10 for orienting and crystallizing the plasticmaterial M coming from the supply openings 6, 7, 8 and 9. The hotplastic material that exits the supply openings is oriented andcrystallized between the extensions 12, 13 and the cold cooling mandrel11. The layer thickness of the plastic material that is to be laminatedand that arrives from each supply opening is preferably about 1 mm.

The beginning of the extrusion conduit 10 is closed with thermalinsulation 14, and at the outlet end of the extrusion conduit there isanother thermal insulation 15 so that no thermal losses would occur inthe areas of the extrusion apparatus where the plastic material M shouldbe in a molten state. After the second thermal insulation 15, the outletend of the extrusion apparatus in turn comprises a cooling nozzle 16 forcooling the finished product that exits the apparatus.

With reference to FIG. 1, it should be noted that in some cases it mightbe preferable to use an arrangement employing several successiveextrusion apparatuses provided with one rotor and comprisingintercooling devices between the extrusion apparatuses, so thatsufficient cooling could be provided between the different layers ofplastic material.

FIG. 2 shows an arrangement with which the process for manufacturing apipe can be started in an apparatus of FIG. 1. The end of the mandrel 11then comprises a cold starting rod 17 that is made of for examplealuminum and that is drawn with a drawing device 18 connected to the endof the extrusion apparatus until the mandrel 11 is in place, whereupon aconnector 19 connected between the mandrel 11 and the starting rod 17disengages the starting rod from the mandrel 11, whereafter acrystallized pipe P begins to be formed.

The mandrel 11 can be cooled by means of water circulation arranged atits end, whereupon the inlet of water is denoted by reference numeral 20and the outlet by reference numeral 21.

For the purpose of cooling the product arriving from the extrusionapparatus, there is a cooling basin 37 before the drawing device.

When existing products are coated, the use of a mandrel 11 is notpossible and therefore the initial cooling of the product to be coatedmust be performed for example by means of a cooling device placed at theinlet end of the extrusion apparatus.

The apparatus according to the invention is particularly applicable forimplementing a method wherein the rotors 1 and 2 are rotated so fastthat the helical orientation of the plastic material has almost the samedirection as the circumference, whereafter the plastic pipe exiting theextrusion apparatus is drawn with the drawing device 18 in such a waythat the orientation of the plastic molecules in the circumferentialdirection is reduced so that the orientation angle of the finishedproduct will be smaller, preferably about 50 to 60°, whereupon theradial strength will be almost double the axial strength.

The apparatus of FIG. 3 differs from the apparatus of FIG. 1 only inthat it comprises one rotor (rotor 1) and correspondingly two stators(stators 3 and 4). With this apparatus it is possible to prepare only atwo-layer pipe, whereas with the apparatus of FIG. 1 a four-layer pipecan be manufactured.

FIGS. 4 to 6 show some embodiments of the rotor extension and itssurroundings. In all these embodiments the cylindrical extension 12, 13of the rotor 1, 2 enlarges substantially conically in the direction offlow of the plastic material M. There are also means 22, 23 forconducting the plastic material flowing in the supply opening 6, 7 atthe back of the rotor to the outer surface of the extension 12, 13 andthus to be mixed with the plastic material flowing in the supply opening8, 9 at the front of the rotor, and means 24 for conducting the plasticmaterial on the outer surface of the extension further through theextension 12, 13 and into its interior. The aforementioned means consistof a stator extension 22 closing the supply opening 6, 7 situated at theback, apertures 23 that pass through the rotor 1, 2 and that areadjacent to the stator extension, and apertures 24 passing through therotor extension 12 and tapering in the direction of flow of the plasticmaterial, i.e. towards the axis of the extruder. The end of theextension 22 is sealed to the frame of the extrusion apparatus in such away that the entire flow of plastic material upstream of the extension22 is transferred to the product to be prepared or coated solely via theapertures 24 of the extension 22. It must be noted that in an apparatuswith several rotors such an arrangement can be provided in one (forexample the last) rotor or in several rotors.

FIG. 4 shows a situation where the plastic material fibers F passingthrough the apertures 24 are spun on a cold pipe P. The spinning mayalso be performed on a cold mandrel (for example the mandrel 11). Inthis case, it may also be possible to use pure polymer.

In the case of FIG. 5, the mixture S of plastic material is crystallizedon a cold mandrel 26 following the stator, and the resultant layer orproduct arrives at the extrusion conduit 25 from which it is pulled out.In this case, the plastic material mixture S is preferably formed of acomposition of LD and HD plastics. An advantageous blending agent to betempered with the matrix plastic is for example liquid crystallinepolymer (LCP plastic) that can be defibered easily. The figure alsoshows how the plastic particles become fiber-like as they pass throughthe apertures 24 in the extension 22.

The example of FIG. 6 differs from FIG. 5 in that in the former figurethe mixture S′ of cross-linked and non-cross-linked plastic material,preferably polyethylene, is heated to the cross-linking temperature bymeans of a hot mandrel 26.

In the apertures 24, i.e. the defibering apertures, where the rateincreases for example to 100-fold, the orientation increasescorrespondingly and the rotating shearing further increases theorientation.

Plastic can be made to flow through the apertures 23 and 24 in such away that there is a smaller pressure on the side of the flow direction.This is achieved in such a way that the flow is throttled on thepressure side, or the supply opening on this side is closed entirely.

It must be noted that the frost line B and the cross-linking line C inFIGS. 5 and 6 are very close to the aforementioned defibering apertures24. In FIG. 4, where the fibers are spun, the adhesion and frost line Ais situated slightly further from these apertures.

The essential feature in the case of FIGS. 4 to 6 is that theviscosities of the plastics do not have to be different, but the dropsstretch due to the increased rate.

It should also be noted that in the case of the conical extruderconcerned, the ratio of the yield and the speed of rotation can beadjusted, so that the fibers can be stretched in the desired manner.

FIGS. 7 and 8 show some additional applications of a conical extruderaccording to the invention. A central hole, i.e. in this case a centralextrusion conduit 10, extending through an extrusion apparatus that isessentially of the kind shown in FIG. 3 comprises an axially movablehollow rod or mandrel 27 which is provided with at least one expansiveseal 28 that is placed against the inner surface of the product to beextruded, i.e. the pipe P, and that comprises at the end a mandrel cone29.

FIG. 7 shows a control cone 30 that has a contracting diameter and thatfollows the mandrel cone 29, and heating/cooling circuits 35 and 36contained in the mandrel cone 29 and the control cone 30 for heatingand/or cooling the cones 29 and 30 and the plastic material passing overthem. The nozzle section 40 of the extrusion apparatus may extend over apart of the ascending cone 29, over the highest point of the cone oreven above it. A duct 41 situated between the nozzle section 40 and thecone 29 may be of even thickness or it may slightly taper towards thetop of the cone 29. After the cone 30 there may be one more seal 28,whereupon lubricating liquid circulation may be arranged between thefirst and the last seal.

FIG. 8 also shows the possible formation of a tempering zone between thetwo seals 28. This is realized by circulating a liquid between the seals28 by means of liquid inlet and outlet openings 32, 34 formed in themandrel 27 and ring grooves 33 connected thereto. The purpose of thering grooves 33 is to circulate the liquid as efficiently as possible.These tempering means are not shown in FIG. 7 for the sake of clarity.

The mandrel 27 of FIGS. 7 and 8 is also used in the orientation of thepipe P, whereupon the mandrel 27 acts partly as an interior temperingmandrel and its motion is utilized especially during the starting.Therefore FIG. 7 shows the starting stage of pipe manufacture and FIG. 8shows a later stage where the pipe that has already been cooled slidesover the mandrel cone 29. The mandrel 27 that is moved in thelongitudinal direction can preferably also be used to adjust the correcttemperature. When the rate of extrusion is high, for example a suitablecross-linking time can be achieved by increasing the length of themandrel 27 to be heated. The temperature can be adjusted either withdirect convection between the outer surface of the mandrel 27 and theinner surface of the pipe P, or then a zone can be separated between theseals 28, in which zone a cooling fluid is circulated at a suitabletemperature. Suitable liquids include for example water, silicone oil orglycol. This arrangement also provides the advantage that the innersurface of the pipe can be provided with a film, which decreases thefriction between the pipe P and the extension 29 of the mandrel.

The essential feature is that the outer diameter of the mandrel 27 isalmost equal to the inner diameter of the plastic pipe P exiting theextrusion conduit 10, so that the pipe P can be allowed to slide alongthe outer surface of the mandrel 27 and a section of the pipe P can thusbe enlarged with the mandrel.

The length of the mandrel 27 and thus the tempering and reaction timeare adjusted according to the rate of extrusion.

The expansive seals 28 are also intended for the purpose that thevariation in the wall thickness of the pipe P can be taken into accountand that the pipe P can be beaded, i.e. oriented, with the seal 28, ifrequired. These seals are thus not intended to be used in the run ofpipes with unequal inner diameters.

As regards FIGS. 7 and 8, it should also be noted that the arrangementdisclosed therein can naturally also be applied in other extrudersaccording to the invention and not only in the exemplary extruder ofFIG. 3.

FIGS. 9 to 13 show some alternative rotor embodiments. FIGS. 9 to 11show how the rotor and/or its extension 12 may comprise apertures 23, 24passing through the rotor or extension for defibering and/or orientingthe plastic material. There may also be apertures 23, 24 in a rotorprovided with a substantially horizontal extension. The rotor of FIGS. 9to 11 may also be extended by means of an annular flange 38, as shown inFIG. 12, that may comprise defibering and/or orienting openings 39. Theflange 38 may also be attached to a rotor comprising no extension, asshown in FIG. 13.

The invention is described above only by way of example, and a personskilled in the art can implement the details thereof in severalalternative manners within the scope of the appended claims. Therefore,for example the number of the rotors may vary as the need arises, andthere may be intercooling apparatuses 50 between the rotors, ifnecessary, for ensuring that the orientation of the thin plastic layersis frozen. Moreover, the inlet end of the extrusion conduit 10 maycomprise a cooling device 52 for the initial cooling of the productconducted into the conduit.

What is claimed is:
 1. An extrusion apparatus comprising: (a) at leastone conical stator; (b) at least one conical rotor, said rotorcomprising orienting means for defibering or orienting a plasticmaterial; (c) conduit means defining an opening in the apparatus forreceiving an elongate product or mandrel, said conduit means beingdisposed in the apparatus such that, with the product or mandrelreceived in the opening, an extrusion conduit is defined in the openingbetween the product or mandrel and the rotor and stator, said rotor andstator being disposed with respect to one another to form a supplyopening wherein the plastic material flows between the stator and rotorand is pressed into the extrusion conduit, said orienting means beingdisposed at an end of the rotor proximate to the extrusion conduit, saidorienting means comprising a substantially cylindrical extensionextending to the extrusion conduit and disposed at the end of the rotor.2. An extrusion apparatus according to claim 1, wherein said orientingmeans comprise a plurality of apertures passing through the rotor.
 3. Anextrusion apparatus according to claim 1, wherein said orienting meanscomprise a plurality of apertures passing through the cylindricalextension.
 4. An extrusion apparatus according to claim 1 comprising anannular flange at the end of the cylindrical extension.
 5. An extrusionapparatus according to claim 4, wherein the annular flange comprises aplurality of openings passing through it.
 6. An extrusion apparatusaccording to claim 1, wherein the cylindrical extension enlargessubstantially conically in the direction of flow of the plasticmaterial, said apparatus comprising first means for conducting plasticmaterial flowing in the supply opening from a back of the rotor to anouter surface of the cylindrical extension for mixing with plasticmaterial flowing in the supply opening at a front of the rotor, andsecond means for conducting plastic material on the outer surface of thecylindrical extension through the cylindrical extension and into aninterior of the cylindrical extension.
 7. An extrusion apparatusaccording to claim 6, wherein the first and second means collectivelycomprise a stator extension disposed in back of the rotor that obstructsthe supply opening and a plurality of apertures passing through thecylindrical extension.
 8. An extrusion apparatus according to claim 1,wherein the apparatus also comprises at least a second rotor and asecond stator, said at least one stator and second stator surroundingthe at least one rotor, said apparatus further comprising means forrotating the at least one rotor and second rotor in opposite directions.9. An extrusion apparatus according to claim 8, further comprising meansdisposed between the at least one rotor and the second rotor for coolingplastic material pressed into the extrusion conduit whereby to fix theorientation of the plastic material.
 10. An extrusion apparatusaccording to claim 1, comprising the elongate product received in theopening and cooling means at an inlet end of the extrusion conduit foran initial cooling of plastic material pressed into the conduit.
 11. Anextrusion apparatus according to claim 1, comprising the mandrelreceived in the opening, said mandrel being heated or cooled.
 12. Anextrusion apparatus according to claim 11, wherein the mandrel is anaxially movable rod that extends through the extrusion apparatus andthat comprises at its end a mandrel cone, said mandrel being heated orcooled.
 13. An extrusion apparatus according to claim 12, wherein therod comprises at least one seal that is expandable against an innersurface of either the extrusion apparatus or plastic material to beextruded.
 14. An extrusion apparatus according to claim 13, wherein therod is hollow and the apparatus further comprises a second seal, meansfor warming or cooling the rod or both, means for expanding the at leastone seal, and means for forming a tempering zone between the at leastone seal and the second seal.
 15. An extrusion apparatus according toclaim 1 comprising, at an outlet end of the extrusion conduit, thermalinsulation and a cooling nozzle.
 16. A method for orienting plasticmaterial during the formation or coating of a cylindrical plasticproduct comprising: (a) providing an extrusion apparatus comprising atleast one conical stator, at least one conical rotor comprising meansfor defibering or orienting the plastic material, an extrusion conduitand a supply opening between the stator and the rotor from which theplastic material is pressed into the extrusion conduit; (b) introducingthe plastic material into the supply opening and rotating the at leastone rotor sufficiently rapidly to impart to molecules of the plasticmaterial a helical orientation having a direction that is almost thesame as a circumference of the cylindrical plastic product; and (c)drawing the oriented plastic material from the extrusion apparatus in away that reduces the orientation of the plastic molecules in thecircumferential direction whereby the cylindrical plastic product or acoating thereon has an orientation angle that is smaller than that ofthe oriented plastic material.
 17. A method according to claim 16,wherein the drawing in step (c) comprises drawing the oriented plasticmaterial over a tempered mandrel to stretch the plastic moleculessimultaneously in the circumferential direction and in an axialdirection.
 18. A method according to claim 16, wherein the plasticmaterial comprises fibers, said method comprising coating thecylindrical plastic product by passing said product through theextrusion apparatus and spinning and crystalizing the fibers of theplastic material thereon with cooling of the product.
 19. A methodaccording to claim 16, wherein the plastic material is a mixture ofcrosslinked material and the method comprises heating the mixture to acrosslinking temperature with a hot mandrel.
 20. A method according toclaim 17, comprising adjusting the length of the tempered mandrel.
 21. Amethod according to claim 16, comprising tempering the oriented plasticmaterial by decreasing a temperature thereof in a tempering zone.
 22. Amethod according to claim 21, wherein the temperature is decreased byincreasing a length of the tempering zone.